Soil exploitation strategies of fine roots in different tree species of the southern boreal forest of eastern Canada

This study compared the ability of conifers (Abies balsamea (L.) Mill., Picea glauca (Moench) Voss) and deciduous trees (Populus tremuloides Michx., Betula papyrifera Marsh.) and shrubs and herbs to exploit soils in a southern boreal forest. Root samples were collected from undisturbed soil and ingrowth cores (disturbed soil) of aspen-and conifer-dominated plots. Total fine-root biomass was similar in aspen and conifer plots but length density was higher under aspen. The low root length density (0.7 cm.cm(-3)) of conifers suggests a dependency on mycorrhizal associations for effective nutrient uptake. Coniferous fine roots were thicker than in the ether species. Root tip and internode lengths in deciduous trees showed little differences between undisturbed and disturbed soil, whereas these parameters increased substantially in conifers in disturbed soil. Root growth and architecture in disturbed soil indicated that conifers follow a conservative strategy of optimizing soil exploitation efficiency through the relatively slow development of coarse fine-root systems. In contrast, deciduous trees and understorey shrubs and herbs colonized favourable soil environments to a larger extent maintaining highly ramified thin fine rests to optimize the exploited soil volume. The different soil exploitation strategies may be as important as those differences reported for aboveground growth to explain the coexistence of these species.